1. Field of Invention
The invention relates to a light-splitting device and more particularly to a light-splitting device, which is used in a projection system.
2. Related Art
The projection systems are divided into three types including a liquid crystal display (LCD) type, a liquid crystal on silicon (LCoS) type, and a digital light processing (DLP) type. The DLP type has several advantages, including high brightness, accurate tone reproduction, fast response time, noise-free operation, and thin and light composition. Therefore, the DLP type is one of the most potential projection technologies recently.
In a DLP projector, a digital control method and a light reflection principle are adopted. First, light rays are integrated or converged by a light integration rod and then pass through the color filter of the color wheel, which splits the light rays. The split light rays are then projected onto a digital micro-mirror device (DMD). In this technology, the DMD is used to replace the liquid crystal panel for representing images in the conventional liquid crystal projector. Since the DMD includes several movable micro-mirrors, driving electrodes may control the tilt angle and deflection time of each movable mirror. Then, the light rays may be projected to form an image by switching the reflection directions of the light rays.
As shown in FIG. 1, FIG. 1 is a lateral view that shows a conventional color wheel assembly. The color wheel assembly 1 mainly includes a color filter 11 and a motor 12. The motor 12 has a housing 121 and a motor body 122. The housing 121 is disposed at one side of the motor body 212. Moreover, the color wheel assembly 1 further includes a fixing plate 13 and a flexible printed circuit (not shown). The color wheel assembly 1 is fixed in a projection system with the fixing plate 13, and the flexible printed circuit electrically connects with a driver. The driver drives the motor body 122 to rotate around the central axis. The motor body 122 is mainly composed of a shell, a magnetic ring, a laminated steel stack and a coil. When the current is applied to the coil, the laminated steel stack produces a magnetic force and a magnetic field. Controlling the positive/negative property and the intensity of the flowing current may change the magnetic field in sequence, so as to produce a rotating magnetic field. Accordingly, the magnetic ring can interact with the magnetic field and thus be driven to rotate. The color filter 11 is fixed on the housing 121 of the motor 12 by way of an adhering process. The motor 12 drives the color filter 11 to rotate around the central axis, so that the color filter 11 may split the light. In the current industry, the color filter 11 may be a ring-shaped filter composed of different color sections for setting on the housing 121 of the motor 12. Further, the color filter 11 is adhered to the housing 121 of the motor 12 with an adhesive, and the adhesive needs to be heated to solidify. However, the heat-resistant temperature of the motor 12 is about 80° C., and the motor 12 may be damaged easily during the heating process. Hence, even only one component of the color wheel assembly 1 is damaged, the whole assembly is unusable. Because of the above reason, the production costs would be increased.
Furthermore, in the projection system, the color wheel assembly 1 is near to a light source. Because of the high operation temperature of the light source, the ambient temperature of the color wheel assembly 1 would also be increased. The heat-resistant temperature of the adhesive is about 150° C. to 180° C., and the operation temperature of the light source is about 150° C. to 200° C. The adhesive is easily fragile under 150° C. to 200° C., so that the adhesion force between the color filter 11 and the motor 12 would be decreased. In general, because the motor 12 for the color wheel assembly 1 rotates at a speed higher than 7200 rpm, the centrifugal force of one section of the color filter 11 is very high. Hence, in this ambient temperature, the rotation center of the color filter 11 is easily away from the central axis of the rotation shaft, and the color filter 11 may produce displacement easily. Further, the reliability of the product would be decreased.
It is therefore a subjective of the invention to provide a light-splitting device to solve the above-mentioned problems.